Parallel and perpendicular polarization of light

[barnali]

Dear Yambo Users,
I am calculating the optical response of a 2D sheet using GW+BSE method. I want to calculate the anisotropy in the optical spectra for in-plane polarization (when the electric field is parallel to the 2D plane) and out of plane polarization (when the electric field is perpendicular to the 2D plane).

My questions are-
How can I calculate the anisotropy in the optical spectra using yambo?

Should I change only the % BLongDir block in BSE calculation? Or I need to change % LongDrXp and % LongDrXs block along with % BLongDir block?


I guess
for in-plane polarization, the % BLongDir will be like

% BLongDir
1.000000 | 0.000000 | 0.000000 | # [BSS] [cc] Electric Field
%
or

% BLongDir
0.000000 | 1.000000 | 0.000000 | # [BSS] [cc] Electric Field
%

and for out of plane polarization, % BLongDir will be like

% BLongDir
0.000000 | 0.000000 | 1.000000 | # [BSS] [cc] Electric Field
%

Cloud anyone please suggest me the appropriate procedure for calculating the anisotropy in the optical spectra for in-plane polarization and out of plane polarization?

Thanking you

Sincerely

Barnali Bhattacharya
Ph. D student (CSIR SRF)
Department of Physics
Assam University, Silchar, India

[Daniele Varsano]

Dear Barnali,
as you argued the % BLongDir block controls the light polarization for the absorption calculations.
About the screening (LongDrXs), this is the direction of the external field needed to calculate the screening: you can set it as (1,1,1) a sort of spatial average, or (1,1,0) as a spatial average in the plane. This should not affect the results.

Best,

Daniele